蒙古后杭爱省楚鲁特铀成矿区地质特征和成因探讨

Discussion on geological features and genesis of Chulute uranium metallogenetic region of North Hanggay Province in Mongolia

楚鲁特铀成矿区位于蒙古后杭爱省北部。大地构造上位于蒙古一外贝加尔褶皱系的最西端。该地区广泛发育铀专属性的花岗岩,其中晚三叠世-早侏罗世花岗岩的铀质量分数为5×10-6 -6×10-6。由于新构造运动的活化,在花岗岩基底上形成了第四纪侵蚀型古河谷,充填了富含有机质的碎屑岩和玄武岩壳。在2条产于花岗岩体的古河谷中,发现了古河谷型铀矿化(达金河矿点、巴雅尔矿点和苏尔矿点),其中以苏尔矿点研究较详细。在宽500 m的范围内见到厚9.1-19.75 m的矿体。铀品位为0.01%-0.05%。铀矿化产于漂白的、褐铁矿化的富含炭质植物碎屑和黑色泥岩薄层的灰色亚砂土、亚粘土和砂中。铀矿物为铀石。苏尔矿床探明的铀资源量为2 500 t,以上2个河谷中总的预测资源量为15 000-16 000 t(P2级)。该地区铀矿化的特点是成矿年龄新,且近源,其形成可能与玄武岩浆喷溢形成的地表热场有关。

Chulute uranium metallogenetic region is situated in the northern part of North Hanggay Province in Mongolia. Geotectonically, it is located at the very western end of Mongolia-Transbaikal fold system. The granite with elevated uranium content is widely developed in this region, where the uranium content in the granite aged from Later Triassic to Early Jurassic ranges from 5×10^-6 to 6 ×10^-6. Due to the neotectonic activation, Quaternary palaeo-valleys that incised the basement were formed on the basement granite and were filled with organic matter-rich elastic sediments and basalt crusts. The palaeo-valley type uranium mineralization （Dajinhe, Bayaer and Shuer uranium occurrences） is discovered in the two palaeo-valleys which incised the granitoids. Of them, Shuer uranium occurrence has been studied more in detail. An ore-body with the thickness from 9. 1 m to 19.75 m has been found in an area with the width of 500 m, and the uranium grade ranging from 0.01% to 0.05 %. The uranium mineralization occurs in the bleached and limonitized grey loam and clayey soil and sand which bear rich calliferous plant debris and lamella of black mudstones. Coffinite is the uranium mineral. The uranium resources in Shuer deposit has been proven as 2 500 t. The total predictive resources in above mentioned two palaeo-valleys reaches as much as 15 000 - 16 000 t （P2）. The uranium mineralization in this region is characterized by young mineralization age and adjacent sources. The ore formation is possibly related to the surface thermal field which is originated from the eruption of the basaltic magmas.